The present invention relates generally to signal generators and more particularly to radar antenna pattern signal generators utilized in electronic test equipment to simulate time varying emissions from a number of different transmitters and where the relative positions of the transmitters or emitters from the receiver may also be varying with time. This type of environment with time varying transmitter parameters and/or time varying transmitter/receiver distances and relative spatial relationships is often referred to a dynamic electromagnetic environment.
One known type of apparatus for simulating in real time the electromagnetic signal received from an RF transmitter in a dynamic electromagnetic environment is disclosed in U.S. Pat. No. 3,719,812 entitled "Dynamic Electromagnetic Environment Simulator" issued to G. Bishop et al. on Mar. 6, 1970 and assigned to the assignee of the present invention. Disclosure therein is a general purpose computer wherein there is stored data relating to the varying relative positions of the environmental emitters and the equipment under test, the parameters of the emission from environmental emitters, the transfer functions of the simulator test equipment hardware, and the characteristics of the equipment under test upstream of the point of insertion of the simulated signals from the test set. The computer is programmed to use this information to provide on a medium, preferably a magnetic tape, binary coded digital information to control the generation by the test equipment signals in real time that would be received by the equipment under test from the emitters in the environment. In performing a simulation, the tape is placed in the test system hardware and run, whereupon the test equipment hardware translates the signals on the tape into a signal simulating the result, at the equipment under test, of the environmental emitters, which resulting signal is fed into the equipment under test as it is being operated in a normal manner. While the simulated radiation signal is being fed in the equipment under test, an operator of the equipment can observe the effect of environmental radiation upon its operation.
More recently fusible link read only memories have been utilized for producing an electronical signal of the desired antenna pattern. Such apparatus is disclosed in U.S. Pat. No. 4,800,476, entitled "Digital Antenna Pattern Generator For Radar Simulation" issued to A. B. Evans on Feb. 15, 1977. In the simulation apparatus disclosed there is a requirement that every pattern to be simulated must first be fed into memory and thereafter read out on demand. It can be seen therefore that such a system requires a relatively large storge capacity since each antenna design, inter alia, must have its own individual or respective "signature" stored in the memory.
It is an object of the present invention therefore to provide a digital antenna pattern generator which obviates the necessity of storing each and every antenna pattern which is to be simulated.
It is another object of the present invention to provide a digital antenna pattern generator which significantly reduces the data storage requirement by synthesizing many different patterns from one generalized pattern stored in memory.